Malachi 4:6 says Elijah will turn the hearts of the fathers to whom?

Answer: Their children

Elijah will turn the hearts of the fathers to their children and the children to their fathers. Luke 1:17 applies this to John the Baptist.

“Behold, I will send you Elijah the prophet before the coming of the great and awesome Day of the LORD. And he will turn the hearts of the fathers to their children, and the hearts of the children to their fathers. Otherwise, I will come and strike the land with a curse.””— Malachi 4:5-6 (BSB)